Use of benzoin gum to inhibit P-glycoprotein-mediated resistance of pharmaceutical compounds

ABSTRACT

A method for increasing bioavailabilty of an orally administered hydrophobic pharmaceutical compound, which comprises orally administering the pharmaceutical compound to a mammal in need of treatment with the compound concurrently with an essential oil or essential oil component in an amount sufficient to provide bioavailability of the compound in the presence of the essential oil or essential oil component greater than bioavailability of the compound in the absence of the essential oil or essential oil component, wherein the essential oil or essential oil component has an activity of at least 10% inhibition at a concentration 0.01 wt. % or less in an assay that measures reduced conversion of cyclosporine to hydroxylated products using an assay system containing 250 μg rat liver microsomes, 1 μM cyclosporine, and 1 μM reduced nicotinamide adenine dinucleotide phosphate (NADPH) in 1 ml of 0.1 M sodium phosphate buffer, pH 7.4.

This application is a 371 of PCT/US96/09607 filed Jun. 7, 1996.

TECHNICAL FIELD

This invention is directed to the field of pharmacology and particularlyto the formulation of oral pharmaceutical compositions for increasedbioavailability and reduced inter- and intra-individual variability.

BACKGROUND

Pharmacokinetics is the study of the fate of pharmaceuticals from thetime they are ingested until they are eliminated from the body. Thesequence of events for an oral composition includes absorption throughthe various mucosal surfaces, distribution via the blood stream tovarious tissues, biotransformation in the liver and other tissues,action at the target site, and elimination of drug or metabolites inurine or bile.

Bioavailability of a drug (pharmaceutical composition) following oraldosing is a critical pharmacokinetic determinant which can beapproximated by the following formula:

    F.sub.oral =F.sub.ABS ×F.sub.G ×F.sub.H

F_(oral) is oral bioavailability fraction, which is the fraction of theoral dose that reaches the circulation in an active, unchanged form.F_(oral) is less than 100% of the active ingredient in the oral dose forfour reasons: (1) drug is not absorbed out of the gut lumen into thecells of the intestine and is eliminated in the feces; (2) drug isabsorded into the cells of the intestine but back-transported into thegut lumen; (3) drug is biotransformed by the cells of the intestine (toan inactive metabolite); or (4) drug is eliminated by the cells of theliver, either by biotransformation and/or by transport into the bile.Thus, oral bioavailability is the product of the fraction of the oraldose that is absorbed (F_(ABS)), the fraction of the absorbed dose thatsuccessfully reaches the blood side of the gastrointestinal tract(F_(G)), and the fraction of the drug in the GI blood supply thatreaches the heart side of the liver (F_(H)). The extent of gut wallabsorption, back transport and metabolism, and liver elimination are allsubject to wide inter- and intra-individual variability.

Previous investigations arising in the laboratory or one of the presentinventors resulted in new understandings of factors involved withbioavailability and in the invention described in U.S. patentapplication Ser. No. 08/190,288, filed Feb. 2, 1994. This applicationdescribed general methods for increasing bioavailability of oralpharmaceutical compositions and methods for identifying compounds thathad increased bioavailability. However, although that invention made itpossible to investigate a number of classes of compounds not previouslythought to be useful in enhancing bioavailability, the actual process ofidentifying specific classes of compounds that are superiorbioenhancers, among those bioenhancers which work to some degree, stillremains a process of investigation and discovery. Within many classes ofsubstances identified as showing beneral bioenhancing effects, there issurprising variance from class member to class member in the extent ofeach compound's bioenhancing effect, and some compounds that would atfirst thought appear to be enhancers of drug bioavailability because oftheir membership in a generally effective class of compounds, actuallyare found to be agents that interfere with the bioavailability of drugs,although the mechanism by which such interference takes place is not yetknown. In some cases, a single compound or small group of compounds hasbeen found to be particularly potent as a bioenhancer despite resemblingin structure other compounds that have less activity or that even reducebioavailability.

Accordingly, it is important to identify and confirm the identity ofclasses of compounds or individual compounds that are particularlyuseful for enhancing bioavailability.

SUMMARY OF THE INVENTION

An object of this invention is to identify compositions with superiorability to increase drug bioavailability, particularly by increasing netdrug absorption and/or decreasing drug biotransformation in the gut wallby inhibiting cytochrome P450 drug metabolism and/or P-glycoprotein(P-gp) drug transport.

Another object of the invention is to provide compositions that stronglyinhibit enzymes of the cytochrome P450 3A class (CYP3A) in the gut inpreference to in other locations, such as the liver, which waspreviously thought to be the primary site of drug metabolism.

A further object of the invention is to provide compositions thatstrongly inhibit P-gp-controlled back transport to increase the nettransport of drugs through the enterocyte layer and cause an increase inthe bioavailability of a coadministered drug, since the protein P-gppumps drugs that have been transported into the cytoplasm of enterocytesback into the lumen of the gut.

One specific object of the present invention is to reduceinter-individual variability of the systemic concentrations of theactive pharmaceutical compound, as well as intra-individual variabilityof the systemic concentrations of the pharmaceutical compound beingadministered.

The invention is carried out by co-administering one or more essentialoils with an oral pharmaceutical compound (drug) or compounds toincrease drug bioavailability. The compositions and methods of theinvention can be used to increase drug efficacy in humans and in othermammals. Although veterinary use is specifically contemplated, theprimary use will be in human treatment. Administration schemes include,but are not limited to, use of oral and topical formulations in humansand use of similar formulations for livestock.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Essential Oils Increase Drug Bioavailability

The present invention arises from continued research into the factorsaffecting drug bioavailability that were described in an earlierapplication arising from the laboratory of one of the present inventors."Drug bioavailability" is defined here as the total amount of drugsystemically available over time. The present invention increases drugbioavailability by inhibiting drug biotransformation in the gut and/orby inhibiting active back transport systems in the gut that decrease thenet transport of drugs across gut epithelia into the bloodstream. Ineither case the composition responsible for increased drugbioavailability is an essential oil. For reasons that are notimmediately apparent, it has been discovered that essential oils, as aclass, are typically capable of inhibiting the appropriate enzyme and/ortransport system, despite the chemical differences that exist among theindividual compounds that are found in the essential oils.

The inventors theorize that the mechanisms for such inhibitory effectmay result directly or indirectly from the course of the mammalianevolution. In general, the botanicals in which the essential oils andessential oil components belong have always been the mainstay of themammalian food supply. To produce an effect, they simply require to beconsumed, and they are consumed directly without preparation (althoughnot in the concentrated form of an essential oil or isolated essentialoil component). In the course of consumption, related biochemicalmechanisms may have evolved for the direct advantage of the mammalianorganism or as an indirect result of evolutionary accident orimperative. Thus, while the essential oils and essential oil componentsevidence chemical differences, the similar source of their origin, thesimilarity of their location in the mammalian food supply, perhaps thesimilarity of their direct or indirect effect on the evolution of themammalian organism, and certainly their similarity in effect on themammalian organism leads to the reasonable conclusion that essentialoils can be considered as a cohesive class of compounds of an importanceeven beyond what ties them together by technical definition, namely thatessential oils are predominately volatile materials or materialsisolated by some physical (as opposed to chemical) process from anodorous, single-species botanical source.

In general, the present invention provides a method for increasing theorganism of an orally administered pharmaceutical compound (particularlyone which is hydrophobic) by orally administering the pharmaceuticalcompound to a mammal in need of treatment concurrently with an essentialoil in sufficient amount to provide integrated systemic concentrationsover time of the compound greater than the integrated systemicconcentrations over time of the compound in the absence of the essentialoil. Changes in the integrated systemic concentrations over time areindicated by "area under the curve" (AUC) measurements, an acceptedpharmacological technique described in detail below.

Essential Oils

For the purposes of this invention, an essential oil is a predominatelyvolatile material or materials isolated by some physical (as opposed tochemical) process from an odorous, single-species, botanical source. Themost widely used process for the isolation of essential oils is steamdistillation of plant matter, although dry distillation and solventextraction are also used. A botanical source is odorous if an odor canbe detected by any animal, not just a human; "odorous" thus is simply anindication that some volatile component is present in the plant. Theoils extracted by the physical process can contain some non-volatilematerial, as is well known in the art. Essential oils have been knownfor centuries in many cases and even millennia, and this term is wellknown in the art. Essential oils are available commercially (even to theextent of being available if carload lots) because of their common useas flavorings for food. The names used for essential oils in Table 1below are commonly recognized commercial names.

Since the individual components of the essential oils are the individualcompounds that will interact with enzymes and transport proteins in themanner described herein, it is apparent that essential oil componentsthat are sufficiently active will also be useful in the practice of theinvention. However, it would be awkward to always refer to "essentialoil or essential oil component," so in this application "essential oil"(or "essential oils") refers to both entire essential oils as obtainedfrom plants and to individual components of essential oils, such asthose listed in Table 2 below. Where more precision is needed to referto components of essential oils as distinct from full essential oilmixtures, the components are expressly referred to. When it isappropriate to distinguish essential oils as a class from "essentialoils and essential oil components," the phrase "essential oil extract"or "full essential oil" is used if the meaning is not clear from thecontext.

Because some few essential oils and essential oil components are of lowactivity and thus not likely to be useful for the purposes describedgenerally herein, only those essential oils and essential oil componentsthat have an activity of at least 10% inhibition at a concentration of0.01 wt. % or less in an assay that measures reduced conversion ofcyclosporine to hydroxylated products using an assay system containing250 μg rat liver microsomes, 1 μM cyclosporine, and 1 mM reducednicotinamide adenine dinucleotide phosphate (NADPH) in 1 ml of 0.1 Msodium phosphate buffer, pH 7.4, are considered to be within the meaningof "essential oil" and thus within the invention as described herein.Preferred are those full oils and components that show an inhibition ofat least 60% at a concentration of 0.01%; more preferred are those fulloils and components that show an inhibition of at least 40% at aconcentration of 0.001%; even more preferred are those full oils andcomponents that show an inhibition of at least 20% at a concentration of0.0001%. A detailed description of this assay system is set out in theexample below.

A number of essential oils are used for their flavors and odors and arerecognized by the Code of Federal Regulations, Title 21, as GRAS(generally recognized as safe) compounds that do not require regulatoryagency approval before they are included in ingested materials. Seeparticularly parts 182.20, 182.40, and 182.50 of 21 CFR. Additionalessential oils and components of essential oils are identified in 21 CFR172.510 and 172.515 as having been used previously in foods, althoughthey are not on the GRAS list. A number of important essential oils areset out in Table 1 below. In this and similar tables showing inhibition,inhibition is measured from the solvent baseline (usually ethanol orother solvents as described below). The reason for higher variability ofresults on repeats for lower concentrations of oils is unknown, but maybe due to evaporation of components when only small amounts are present.

    TABLE 1      - ESSENTIAL OILS            repeat   repeat   repeat      CAS # CFR # Name Latin name 0.01% SD 0.01 (SD) 0.001% SD 0.001 (SD)     0.001% SD 0.0001 (SD) 0.00001% SD      8006-77-7 182.20 Allspice Berry Pimenta officinilis L. 100 0  74 2  32     2        Amber Essence  54 1      84775-42-8 182.20 Anise Seed Pimpinella anisum L. 91 10  29 5      68990-11-4      172.510 Arnica (20%) Arnica spp. 35 3                        8007-00-9     182.20 Balsam of peru Myroxylon percirae obscured   6 3         Klotzsch      8015-73-4 182.20 Basil Ocimum basilicum L. 91 2  59 1      91721-75-4 182.20 Bay Leaf (Myrcia) Pimenta acris Kostel 91.3 0.5  57.9     0.5      9000-05-9  172.510 Benzoin Gum Styrax spp. 100 0  100 0  40 2 22 (3);     -6                  (13)      8007-75-8 182.20 Bergamot Citrus aurantium L. 99 2  46.4 0.2         subsps. bergamia         Wright et Am.      8015-77-8 182.20 Bois de Rose Aniba roscacodora 94.9 0.2 100 (0) 53 3          (Rosewood) Ducke      8008-98-8      172.510 Cajeput Melaleuca ssp. 91.5 0.4  56 4                  182.20     Calendula (Marigold Calendula officinilis 19 6        pot) L.      8008-51-3      172.510 Camphor, White Cinnamonum 89 1 87 (3) 45 5     camphora L. Necs et         Eberm. (Safrole free)      8000-42-8 182.20 Caraway Seed Carum carvi L. 92 4  59 1      8000-66-6 182.20 Cardamon Elleteria cardamomum 99 1 100 (0) 64 1  7 6           (L.) Matoa      8015-88-1 182.20 Carrot Seed Daucus carota L. 100 0  81.6 0.1  52 1 45     (2);3                  (10)      68990-83-0  172.510 Cedarwood Thuja occidentalis L. 100 0  95 4  56 2     74 (1);12         (Thujone free)         (4)      8015-90-5 182.20 Celery Apium graycolens L. 91 3  66 3  17 2      8002-66-2 182.20 Chamomile, German Matricaria chamomilla 98.4 0.2  66 2      17.7 0.4        or Hungarian L.      8015-92-7 182.20 Chamomile, Roman or Anthemis nobilis L. 100 0  69 2     28 4        English      8015-91-6 182.20 Cinnamon Cinnimomum spp. 78 2  29 3      8000-29-1 182.20 Citronella Cymbapogon nardus 91 1  60 4  -6 5         Rendle      8016-63-5 182.20 Clary Sage Salvia aclarca L. 98 2  34 4      8000-34-8  184.1257 Clovebud Eugenia spp. 100 0  84 1  46 4 50.03                        (0.05);6 (3)      8008-52-4 182.20 Coriander Coriandrum sativum 89 2  30 5         L      8014-13-9 182.20 Cumin Cuminum cyminum L. 100 0  52 5      8013-86-3  Cypress Cupressa 92.3 0.5  6 3         sempervirens L.      8000-48-4  172.510 Eucalyptus Eucalyptus globulus 93 1  65 3  23 1              Labille      8006-84-6 182.20 Fennel Foeniculum vulgare 89 3  35 1         Mill. var. dulce D.C.      8021-29-2  Fir needle, Siberian Abica siberica 92 1  79 10  31 2             8016-36-2  172.510 Frankincense Boswellia spp. 97 1  33 1               (Olibanum oil)      8000-78-0      184.1317 Garlic Allium sativum L. 36 1                        8000-46-2     182.20 Geranium, Rose Pelargoneum 92 6  68 3  3.44 0.04         gravcolena L'Her      8007-08-7 182.20 Ginger Zingiber officinaale 100 0 100 (3) 78 2  23 2           Rose.      8016-20-4 182.20 Grapefruit Citrus paradisi Macf. 88 1  29 4      8006-83-5 182.20 Hysaop Hysaopus officinalis L. 98.2 0.1  60 2  14 4         8022-96-6 182.20 Jasmine Absolute Jasminum 95 2  48.4 0.5         grandiflorum L.        Jojoba  1 1      8012-91-7 182.20 Juniper Berry Juniperus communis 96 2  15.9 0.4                L.      8000-28-0 182.20 Lavender Lavandula angustifolia 97.8 0.1  49.5 0.6          8008-56-8 182.20 Lemon Citrus limon (L) 62 4  20 2         Burm. f.      8007-02-1 182.20 Lemongrass Cymbapogon citratus obscured   52 3                 DC. & Cymbopogon         flexuosus      8008-26-2 182.20 Lime Citrus surantifolia 91 1  36 3         (christman) Swingle      8015-01-8 182.20 Marjoram, sweet Marjorana hortensis 94 1  54 3                 Moench (Origanum         marjorana L.)        Mugwort  98 1  65 3  30 3      172.510 Mullein Flower Verbascum spp. 47 5     9000-45-7  172.510 Myrrh Gum Commiphora spp. 100 0  74 3  15 3 13 (1)         8016-38-4 182.20 Neroli, bigarade Citrus surantium L. 98 2  44 4          8008-45-5 182.20 Nutmeg Myristica fragrans 92 2 100 (0) 22.3 0.2            boutt.      8030-28-2 182.20 Orange, Bitter Citrus surantium L. 88 3  23 3      68606-94-0 182.20 Orange, Sweet Citris sinenais (L.) 66 5  33 3                 Osbeck        Oregano Lippia spp. 99.7 0.4 100 (0) 75 2  30 1      8014-09-3  172.510 Patchouly Pogostemon spp. 100 0  99 (3) 100 0  64 4     49 (2); 38 14 2                  (3)      8013-99-8      172.510 Pennyroyal Mentha Pulegium 99 1  57 5                 8006-82-4     182.20 Pepper, Black Piper nigrum L. 98 2  78.3 0.3  6 3      8006-90-4 182.20 Peppermint Mentha piperita L. 98 1 100 (0) 73 3  56 4     47 (1); 41                  (2)      8014-17-3 182.20 Petitegrain Citrus surantium L. 97 1 100 (1) 14 3           8021-29-2  172.510 Pine Needle Abica spp. 93 1 100 (0) 57 3               Poke Root  9 2      8007-01-0 182.20 Rose Absolute Rosa spp. 99 1 100 (0) 40 3      8007-01-0 182.20 Rosechip Seed Rosa spp. 60 5  -5 4      8000-25-7 182.20 Rosemary Rosemarinus 95.5 0.3 100 (0) 56 2         officinalis L.      8016-64-6 182.20 Sage, Dalmation Salvia officinalis L. 98 1 100 (0) 36     1      8006-87-9  172.510 Sandalwood Oil, Santilum album L. 100 0  100 0  95 2     79 (2); 11.9 0.5        Mysore          91.9 (0.4)      8006-80-2  Sassafras Sassafras albidum 93 2      98 (1) 51 5                    (Nutt.) nees      8003-79-5 182.20 Spearmint Mentha spicata L. 98 2  62 6  4 2         (Safrole free)      8022-22-8  Spikenard  obscured  obscured obscured      8008-80-8  172.510 Spruce (Hemlock) Tsuga and Picca spp. 95.9 0.2  35 2      8003-31-9 182.20 Tangerine Citrus reticulata blanco 91.3 0.1 100 (0) 46     3      68647-73-4  Tea Tree Melalcuca alternifolia 95.8 0.2  98 (4) 49 4            8007-20-3  172.510 Thuja (Cedar leaf) Thuja occidentalis 95 1 100     (0) 66 4  23 4      8007-46-3 182.20 Thyme Thymua vulgaris L. 97.3 0.5 100 (0) 38 4              84650-63-5 182.20 Vanilla Extract Vanilla spp. 6 2      8016-96-4  172.510 Vetivert Vetiveria zizanioides obscured   obscured           Stapf.      90045-28-6 182.20 Wintergreen Gaultheria procumbens 87 1 100 (0) 9 5            L.        Witch Hazel  2 6        (Hamamelia) Extract      8006-81-3 182.20 Ylang Ylang Cananga odorata Hook 100 0  83 1  40 3 43     (4); -5        (Cananga) Extract f. and Thomas         (11)

    TABLE 2      - OIL INGREDIENTS            repeat 0.01   repeat 0.001   repeat      CAS # CFR # Name Other names 0.01% SD (SD) 0.001% SD (SD) 0.0001% SD     0.0001 (SD)      3016-19-1  Allo Ocimene 2,6-Dimethyl-2,4,6-octatriene not tested   22 4      6 1      4180-23-8 182.60 Anethole, trans- 4-Propenylanisole 100 0  53 2              103-41-3 172.515 Benzyl Cinnamate Benzyl 3-phenylpropenoic acid     not tested   -45 6  7 2      464-45-9 172.515 Borneol-(IS)-endo(-) 1,7,7-Trimethylbicyclo 2.2.1! 100     0  80 3  20 3         heptan-2-ol      5794-03-6 172.515 Camphene-(+) 2,2-Dimethyl-3- not tested   12.4 0.9     -49 19         methylenebicyclo 2.2.1!heptane      21368-68-3 172.515 Camphor-(±) 1,7,7-Trimethylbicyclo 2.2.1! 87 3     57 4 53 (3)         heptan-2-one      404-86-4  Capsaicin trans-8-Methyl-N-vanillyl-6 not tested   68 2  27 3         nonenamide      13466-78-9  Carene-3-(Δ) 2,2,5-Trimethlbicyclo 4.1.0! not tested      34 4  -26 5         hept-5-one      499-75-2 172.515 Carvacrol 5-isoPropyl-2-methylphenol 97 1  93 1  11 1       99-48-9 172.515 Carveol-(-) p-Mentha-6,8-dien-2-ol not tested   60 1     2 2      6485-40-1 182.60 Carvone-(R)-(-) p-Mentha-6,8-dien-2-one 100 0  69 2     27 4      2244-16-8 182.60 Carvone-(S)-(+) p-Mentha-6,8-dien-2-one not tested     70.5 0.1  30 2      87-44-5 172.515 Caryophyllene, trans-(-) β     Caryophyllene not tested   85 2  26 3      14371-10-9 182.60 Cinnamic Aldehyde, 3-Phenylpropenaldehyde 78 1  29.0     0.6        trans-      5392-40-5 182.60 Citral Mixed geranial and neral 99 1  54 3  44 2     obscured      2385-77-5 172.515 Citronellal-(R)-(+) 3,7-Dimethyl-6-octenal 95 4  71 2      30 1 20 (4)      5949-05-3 172.515 Citronellal-(S)-(-) 3,7-Dimethyl-6-octenal 100 0  62     2  -1 1      106-22-9 172.515 Citronellal-(DL)-(β) 3,7-Dimethyl-6-octen-1-ol 95     2  86 1  41 1 35 (4)      140-67-0 172.515 Entragole 4-Allylanisole 100 0  69.2 0.6  7 2      103-36-6 172.515 Ethyl Cinnamate, trans- Ethyl 3-phenylproponoic acid     not tested   -16 8  -13 8      121-32-4 182.60 Ethyl Vanillin 3-Ethoxy-4-hydroxybenzoledhyde 58 1           470-82-6 172.515 Eucatyptol 1,8-Cincole 88 1  64 3  38 1      97-53-0 184.1257 Eugenol 4-Allyl-2-methoxyphenol 100 0  66 1  9.8 0.4        106-28-5 172.515 Farnesol, trans-, trans- 3,7,11-Trimethyl-2,6,10-     not tested   82 3  49 4         dodecatrien-1-ol      2217-02-9 172.515 Fenchol-(IR)-endo-(+) 1,3,3-Trimethylbicyclo 2.2.1!     100 0  74 1  18 2         heptan-2-ol      7787-20-4 172.515 Fenchone-(IR)-(-) 1,3,3-Trimethylbicyclo 2.2.1! not     tested   38 5  14 3         heptan-2-one      106-24-1 182.60 Geraniol trans-3,7-Dimethyl-2,6- 76 7  66.7 0.5  40 2     25(1); -7 (8)         octadien-1-ol      105-87-3 182.60 Geranyl Acetate trans-3,7-Dimethyl-2,,6- 73 8  51.5 0.1         octadien-1-yl acetate      488-10-8 172.515 Jasmone, cis- 3-Methyl-2-(2-pentenyl)-2- not tested     68 1  16.0 0.4         cyclopenten-1-one      5989-27-5 182.60 Limonene-(R)-(+) p-Mentha-1,8-diene 84 3  20 4              5989-54-8 182.60 Limonene-(S)-(-) p-Mentha-1,8-diene 82.3 0.4     30 5      78-70-6 182.60 Linalcol-(±) 3,7-Dimethyl-1,6-octadien-3-ol 85 1     72.0 0.1  41 2 -7 (9); -5 (2)      115-95-7 182.60 Linalyl Acetate 3,7-Dimethyl-1,6-octadien-3-yl 100 0     55.8 0.7         acetate      15356-70-4 182.20 Menthol-(±) p-Menthan-3-ol 100 0  79 2  20 4            14073-97-3 172.515 Menthone-(-) p-Menthan-3-one not tested   52 3      14 3      134-20-3 182.60 Methyl Anthranilate Methyl 2-aminobenzoate not tested     23 1  -7 6      1211-29-6  Methyl Jasmonate-(±) Methyl-3-oxo-2-(2-pentenyl)- not     tested   65 2  -27 5         cyclopentane acetate      119-36-8  Methyl Salicylate Methyl-2-hydroxybenzoate 86 1  12 3              123-35-5 172.515 Myrcene-β 7-Methyl-3-methylene-1,6- not     tested   13 2  0 1         octadiene      106-25-2 172.515 Nerol cis-3,7-dimethyl-2,6-octadien-1- 100 0  81.0 0.6      54 4 37 (2); 12 (2)         ol      7785-70-8 172.515 Pincno-(+)-α 2,6,6-Trimethylbicyclo 3.1.1! not     tested   23 2  -9 3         hept-2-ene      18172-67-3 172.515 Pinene-(IS)-(-)-β 6,6-Dimethyl-2- 88 3  60 2     -10 1         mehylenebicyclo 3.1.1!heptane      89-82-7 172.515 Pulegone-(R)-(+) p-Menth-4-(8)-en-3-one not tested   31     4  -17 5      562-74-3  Terpinen-4-ol p-Menth-1-en-4-ol 100 0  80 2  3.81 0.03             99-86-5 172.515 Terpinene-α p-Mentha-1,3-diene not tested      28 5  -6 5      10482-56-1 172.515 Terpincol-α p-Menth-1-en-8-ol 100 0  86 3     13.4 0.2      89-83-8 172.515 Thymol 2-isoPropyl-5-methylphenol 100 0  56 2

                                      TABLE 3    __________________________________________________________________________    REFERENCE COMPOUNDS    CAS #        CFR #             Name   Other names                          %    0.01%                                   SD repeat (SD)    __________________________________________________________________________    64-17-5        184.1293             Ethanol                    Ethyl alcohol                          1    44  4  42 (4); 49 (4); 45 (8)    64-17-5        184.1293             Ethanol      0.5    33.2                                     0.2             Ketoconazole 0.00005                               100 0             Ketoconazole 0.00001                               42  3             Ketoconazole 0.000005                               20  3             Ketoconazole 0.000001                                8  3    __________________________________________________________________________

Surprisingly, it has also been discovered that individual components ofessential oils tested to date (Table 2) are often not as effective inenhancing bioavailability as the essential oils themselves, which areusually complex mixtures of compounds (usually hydrocarbons andoxygenated hydrocarbons). Thus the essential oils appear to be operatingas synergistic compositions, perhaps because of the ability of differentcomponents of the oils to inhibit different biological pathwaysassociated with bioavailability. While the inventors do not wish to bebound by speculation, it is possible that minor components present inessential oils of all plants may be involved; it is known for examplethat many essential oil components are terpene derivatives, and theremay be identical or structurally similar minor components present inmost if not all plant oils. Thus full essential oils represent onepreferred embodiment of the invention.

As is apparent, since use of one essential oil that contains numerouscomponents and is a mixture is within the scope of the presentinvention, use of a mixture of essential oils (and/or components) willalso be within the scope of the invention.

Bioavailability Measurements

The increase in drug bioavailability attributable to administration ofthe essential oil can be determined by measuring total systemic drugconcentrations over time after coadministration of a drug and theessential oil and after administration of only the drug. The increase indrug bioavailability is defined as an increase in the Area Under theCurve (AUC). AUC is the integrated measure of systemic drugconcentrations over time in units of mass-time/volume. The AUC from timezero (the time of dosing) to time infinity (when no drug remains in thebody) following the administration of a drug dose is a measure of theexposure of the patient to the drug. When efficacy of the essential oilis being measured, the amount and form of active drug administeredshould be the same in both the coadministration of drug and essentialoil and the administration of the drug alone. For instance,administration of 10 mg of drug alone may result in total systemic drugdelivered over time (as measured by AUC) of 500 μg-hr/ml. Incoadministration (i.e., in the presence of the essential oil) thesystemic drug AUC may increase to 700 μg-hr/ml. If significantlyincreased drug bioavailability in the presence of the essential oil isanticipated, drug doses may need to be reduced for safety.

Systemic drug concentrations are measured using standard in vitro or invivo drug measurement techniques. "Systemic drug concentration" refersto a drug concentration in a mammal's bodily fluids, such as serum,plasma or blood; the term also includes drug concentrations in tissuesbathed by the systemic fluids, including the skin. Systemic drugconcentration does not refer to digestive fluids. The increase in totalsystemic drug concentrations is one way of defining an increase of drugbioavailability due to coadministration of essential oil and drug. Fordrugs excreted unmetabolized in the urine, an increased amount ofunchanged drug in the urine will reflect the increase in systemicconcentrations.

Characteristics of Drugs Used With Essential Oils

The word "drug" as used herein is defined as a chemical capable ofadministration to an organism which modifies or alters the organism'sphysiology. More preferably the word "drug" as used herein is defined asany substance intended for use in the treatment or prevention ofdisease. Drug includes synthetic and naturally occurring toxins andbioaffecting substances as well as recognized pharmaceuticals, such asthose listed in "The Physicians Desk Reference," 49th edition, 1995,pages 101-338; "Goodman and Gilman's The Pharmacological Basis ofTherapeutics" 8th Edition (1990), pages 84-1614 and 1655-1715; and "TheUnited States Pharmacopeia, The National Formulary", USP 23 NF 18(1995), the compounds of these references being herein incorporated byreference. The term drug also includes compounds that have the indicatedproperties that are not yet discovered or available in the U.S. The termdrug includes pro-active, activated and metabolized forms of drugs. Thepresent invention can be used with drugs consisting of charged,uncharged, hydrophilic, zwitter-ionic, or hydrophobic species, as wellas any combination of these physical characteristics. A hydrophobic drugis defined as a drug which in its non-ionized form is more soluble inlipid or fat than in water. A preferred class of hydrophobic drugs isthose drugs more soluble in octanol than in water.

Compounds (or drugs) from a number of classes of compounds can beadministered with an essential oil, for example, but not limited to, thefollowing classes: acetanilides, anilides, aminoquinolines, benzhydrylcompounds, benzodiazepines, benzofurans, cannabinoids, cyclic peptides,dibenzazepines, digitalis gylcosides, ergot alkaloids, flavonoids,imidazoles, quinolines, macrolides, naphthalenes, opiates (ormorphinans), oxazines, oxazoles, phenylalkylamines, piperidines,polycyclic aromatic hydrocarbons, pyrrolidines, pyrrolidinones,stilbenes, sulfonylureas, sulfones, triazoles, tropanes, and vincaalkaloids.

Increased Drug Bioavailability by Inhibition of Cytochrome P450

Phase I Biotransformation

Reduction of enterocyte cytochromes P450 participation in drugbiotransformation is one objective of the present invention. The majorenzymes involved in drug metabolism are present in the endoplasmicreticulum of many types of cells but are at the highest concentration inhepatocytes. Traditionally, enterocyte biotransformation was consideredof minor importance in biotransformation compared to the liver. Manycompounds inhibit cytochrome P450. These include, but are not limitedto, ketoconazole, troleandomycin, gestodene, flavones such as quercetinand naringenin, erythromycin, ethynyl estradiol, and prednisolone. Thefirst goal of the invention is to use an essential oil to inhibit drugcytochrome P450 biotransformation in the gut to increase drugbioavailability.

Types Of Cytochromes And Tissue Location

The cytochromes P450 are members of a superfamily of hemoproteins. Theyrepresent the terminal oxidases of the mixed function oxidase system.The cytochrome P450 gene superfamily is composed of at least 207 genesthat have been named based on their evolutionary relationships. For thisnomenclature system, the sequences of all of the cytochrome P450 genesare compared, and those cytochromes P450 that share at least 40%identity are defined as a family (designated by CYP followed by a Romanor Arabic numeral, e.g. CYP3), further divided into subfamilies(designated by a capital letter, e.g. CYP3A), which are comprised ofthose forms that are at least 55% related by their deduced amino acidsequences. Finally, the gene for each individual form of cytochrome P450is assigned an Arabic number (e.g. CYP3A4).

Three cytochrome P450 gene families (CYP1, CYP2 and CYP3) appear to beresponsible for most drug metabolism. At least 15 cytochromes P450 havebeen characterized to varying degrees in the human liver. Atconcentrations of the substrates found under physiologic conditions,enzyme kinetics often favor a single form of cytochrome P450 as theprimary catalyst of the metabolism of a particular drug or other enzymesubstrate.

The CYP3 gene family encoding cytochromes P450 of type 3 is possibly themost important family in human drug metabolism. At least 5 forms ofcytochrome P450 are found in the human 3A subfamily, and these forms areresponsible for the metabolism of a large number of structurally diversedrugs. In non-induced individuals 3A may constitute 15% of the P450enzymes in the liver. In enterocytes, members of the 3A subfamilyconstitute greater than 70% of the cytochrome-containing enzymes. Thefirst two human 3A subfamily members identified were 3A3 and 3A4. Thesetwo cytochromes P450 are so closely related that the majority of studiesperformed to date have not been able to distinguish their contributions,and thus they are often referred to as 3A3/4. ErythromycinN-demethylation, cyclosporine oxidation, nifedipine oxidation, midazolamhydroxylation, testosterone 6β-hydroxylation, and cortisol6β-hydroxylation are all in vitro probes of 3A3/4 catalytic activity.The levels of 3A3/4 vary by as much as 60-fold between human livermapproacal samples, with the levels of 3A forms approaching 50% of thetotal cytochrome P450 present in human liver samples from individualsreceiving inducers of 3A3/4. The recently studied CYP3A5 may also play arole as important as 3A3/4.

The liver contains many isoforms of cytochrome P450 and can biotransforma large variety of substances. The enterocytes lining the lumen of theintestine also have significant cytochrome P450 activity, and thisactivity is dominated by a single family of isozymes, 3A, the mostimportant isoforms in drug metabolism.

Increased Drug Efficacy By Reducing CYP3A Drug Biotransformation

Preferred essential oils of the invention reduce drug biotransformationin the gut by inhibiting CYP3A activity in gut epithelial cells whichleads to a total increase in drug bioavailability in the serum. In thepresence of essential oils, fewer drug molecules will be metabolized byphase I enzymes in the gut and will not be available for phase IIconjugation enzymes. This will lead to increased concentrations ofuntransformed drug passing from the gut into the blood and onto othertissues in the body.

Although the primary objective of the essential oil is to inhibit CYP3Adrug biotransformation in the gut, some biotransformation may bedecreased in other tissues as well if the essential oil is absorbed intothe blood stream. The decrease in biotransformation by other tissueswill also increase drug bioavailability. The advantage of targeting aessential oil to the gut, however, is that it allows the use of lowersystemic concentrations of essential oil compared to inhibitors thattarget CYP3A in the liver. After oral administration of an essentialoil, concentrations will be highest at the luminal surface of the gutepithelia, not having been diluted by systemic fluids and the tissues ofthe body. Luminal concentrations that are greater compared to bloodconcentrations will permit preferential inhibition of CYP3A in gutinstead of the liver. Essential oils that preferentially inhibit gutCYP3A will also be a particularly effective means of increasing drugbioavailability while minimizing the effects of greater concentrationsof essential oils in tissues other than the gut.

Coadministration of an essential oil will also reduce variability oforal bioavailability. Reduction of drug biotransformation or increaseddrug absorption will decrease variability of oral bioavailabillty tosome degree because the increase in bioavailability will begin toapproach the theoretical maximum of 100% oral bioavailability. Theincrease in oral bioavailability will be generally larger in subjectswith lower oral bioavailability. The result is a reduction ininter-individual and intra-individual variation. Addition of essentialoil will reduce inter-individual and intra-individual variation ofsystemic concentrations of a drug or compound.

A Net Increase in Drug Bioavailability Due to a Decrease in the Activityof CYP3A

The catalytic activities of CYP3A that are subject to inhibitioninclude, but are not limited to, dealkyase, oxidase, and hydrolaseactivities. In addition to the different catalytic activities of CYP3A,different forms of CYP3A exist with a range in molecular weight (forexample, from 51 kD to 54 kD, as shown in Komori et al., J. Biochem.1988, 104:912-16).

Some essential oils reduce CYP3A drug biotransformation by acting eitheras an inhibitor of CYP3A activity or as a substrate of CYP3A activity.The essential oil acting either as the inhibitor or the substrate ofCYP3A (or a component of the essential oil) can act as a competitive,non-competitive, uncompetitive, mixed or irreversible inhibitor of CYP3Adrug biotransformation. Additionally, the essential oil can haveproperties of being a ligand for P-gp or cytochrome P450 or a ligand foreither protein.

Selection of Essential Oils by Reduction of CYP3A Drug Biotransformation

The relative ability of compounds to act as bioenhancers and to increasedrug bioavailability can be estimated using in vitro and in vivo drugbiotransformation measurements. In vivo measurements of drugbioavailability, such as measuring serum or blood drug concentrationsover time, provide the closest measure of total drug systemicavailability (bioavailability). In vitro assays of CYP3A metabolism andP-gp-transport, as discussed below, indirectly indicate drugbioavailability because CYP3A drug metabolism and P-gp drug transportaffect integrated systemic drug concentrations over time. Generally, theability of a compound being tested to act as an essential oil isdemonstrated when the addition of the oil to a drug biotransformationassay decreases CYP3A drug biotransformation. Although even a minimallymeasured increase is all that is required for an essential oil to beuseful, a preferred commercially desirable essential oil acting as aCYP3A modulator generally will increase drug bioavailability by at least10%, preferably by at least 50%, and more preferably by at least 75% ofthe difference between bioavailability in the presence of the essentialoil and total availability of the ingested dosage in the absence of theessential oil. A sufficient amount of orally administered essential oilwill provide integrated systemic drug concentrations over time greaterthan the integrated systemic drug concentrations over time in theabsence of essential oil. The actual amount of essential oil to beincluded in a pharmaceutical composition will vary with the oil and theactive ingredient being protected. The amount of the essential oil willgenerally be sufficient to provide a concentration in the gut (and/orvolume, depending on the desired effect) of from 0.00001 wt. % to 0.01wt. %. Examples of individual essential oils and appropriateconcentrations for an effective dosage are set forth in Table 1. Suchamounts will generally be effective, although optimization of thepharmaceutical composition to provide maximum bioavailability should becarried out using the AUC methods described herein, once the componentsfor a particular pharmaceutical composition have been decided upon.

Essential oils that are particularly good inhibitors of enzymes of theP450 3A class can be identified by a variety of bioassays, several ofwhich are set out below.

In vitro CYP3A Assays and Increased Drug Bioavailability

Cell Assays of CYP3A Function and Increased Drug Bioavailability

Cultured cells of either hepatocytes or enterocytes or freshly preparedcells from either liver or gut can be used to determine the activity ofan essential oil as a CYP3A inhibitor. Various methods of gut epithelialcell isolation can be used such as the method of Watkins et al., J.Clin. Invest. 1985; 80:1029-36. Cultured cells, as described inSchmiedlin-Ren et al., Biochem. Pharmacol, 1993; 46:905-918, can also beused. The production of CYP3A metabolites in cells can be measured usinghigh pressure liquid chromatograph (HPLC) methods as described in thefollowing section for microsome assays of CYP3A activity.

Microsome Assays of CYP3A Function and Increased Bioavailability

Microsomes from hepatocytes or enterocytes will be used for assays ofCYP3A activity. Microsomes can be prepared from liver using conventionalmethods as discussed in Kronbach et al., Clin. Pharmacol. Ther 1988;43:630-5. Alternatively, microsomes can be prepared from isolatedenterocytes using the method of Watkins et al., J. Clin. Invest. 1987;80:1029-1037. Microsomes from gut epithelial cells can also be preparedusing calcium precipitation as described in Bonkovsky et al.,Gastroenterology 1985; 88:458-467. Microsomes can be incubated withdrugs and the metabolites monitored as a function of time. In additionthe levels of these enzymes in tissue samples can be measured usingradioimmunoassays or western blots. Additionally, the production ofmetabolites can be monitored using high pressure liquid chromatographysystems (HPLC) and identified based on retention times. CYP3A activitycan also be assayed by calorimetrically measuring erythromycindemethylase activity as the production of formaldehyde as in Wrighton etal., Mol. Pharmacol. 1985; 28:312-321 and Nash, Biochem. J. 1953;55:416-421.

Characteristics of Essential oils that Reduce CYP3A Drug Metabolism

Preferred essential oil(s) will bind CYP3A quickly and inhibit while thedrug is passing through the enterocyte. After the essential oils reachthe heart and are distributed throughout the body the concentrations ofthe essential oils will be diluted on future passes through the liver.Concentrations of essential oil used in the gut lumen are preferablyselected to be effective on gut CYP3A metabolism but, due to dilution,to be less active in other tissues.

The amount of essential oil used for oral administration can be selectedto achieve small intestine luminal concentrations of at least 1/10 ofthe K_(i) for CYP3A inhibition of drug metabolism or an amountsufficient to increase systemic drug concentration levels, whichever isless. Alternatively, the amount of an inhibitor of cytochrome P450 3Aenzyme that will be used in a formulation can be calculated by variousassays that are described in detail below. For example, one such assaymeasures the conversion of cyclosporine to hydroxylated products in anassay system containing 100 μg human liver microsomes, 25 μMcyclosporine, and an NADPH regenerating system in 100 μl of 0.1 M sodiumphosphate buffer, pH 7.4. The initial inhibitor amount is selected toprovide concentrations in the lumen of the small intestine equal orgreater than concentrations that reduce the rate of conversiondetermined by this assay, preferably a rate reduction of at least 10%.While the actual dose of inhibitor in a clinical formulation might beoptimized from this initial dosage depending on the results of aclinical trial, the assay as described is sufficient to establish autilitarian dosage level.

Increased Drug Bioavailability by Inhibition of P-glycoprotein (P-gp)

Increased Drug Absorption By Decreasing P-gp Drug Transport

Essential oils can further increase bioavailability by increasing netdrug absorption in the gut. An essential oil will reduce P-gp activedrug transport in order to increase the net transport of drugs acrossthe gut epithelium. Epithelia exist in a number of different tissuetypes including, but not limited to, the epithelia of the skin, liver,kidneys, adrenals, intestine, and colon. Such epithelia would also beaffected by systemic administration of P-gp inhibitors, but the majoreffects of the oils will be limited to the gut because of concentrationeffects resulting from oral delivery.

Because of the many different compounds present in essential oils aswell as the many different classes of active pharmaceutical compoundswith which they can be used, the oral dosage of both oil and activeingredient present in the formulation (or elsewise as described below)is best determined empirically, as the dosage will depend on theaffinity of the inhibitor for P-gp relative to the drug's affinity forP-gp. There are a number of assays available that allow the desireddosage to be readily determined without requiring clinical trials. Whilethe actual dosage of inhibitor in a clinical formulation might beoptimized from this initial dosage depending on results of a clinicaltrial, the assay as described is sufficient to establish a utilitariandosage level.

Selection of Essential Oils by Reduction of P-gp Drug Transport/Activity

The relative ability of essential oils and to increase drugbioavailability can be estimated using in vitro and in vivo drugtransport measurements. Preferred essential oils will cause a netincrease in drug diffusion resulting from a decrease in active P-gp drugtransport activity. The activity of P-gp can be measured either asATP-dependent membrane transport of a drug or as drug-dependent ATPhydrolysis. P-gp activity or drug flux can be measured using in vitro orin vivo techniques using, but not limited to, voltage-sensitiveelectrodes or dyes, chemical-sensitive electrodes or dyes, substrate orproduct analysis, electron microscopy, or coupled assays. The apparentmolecular weight of P-gp used in the assay will vary depending on thespecies, isoform, amount of glycosylation, and molecular weight assaymethod. Typically, the molecular weight of the P-gp will beapproximately 170 kilodaltons.

The essential oil (or one or more of its components), acting as eitherthe inhibitor or the substrate of P-gp, acts as a competitive,uncompetitive, non-competitive, mixed or irreversible inhibitor of P-gpdrug transport. The essential oil, as an inhibitor or substrate of P-gp,can be either a transportable or non-transportable ligand of P-gp. Theessential oil (or component) can bind to the P-gp on its lumenaccessible surface, cytoplasmic accessible surface or membrane spanningregion. The essential oil can be a ligand of P-gp, a ligand ofcytochrome P450, or a ligand of both, or any combination of the threetypes of ligands. For example an essential oil can comprise a ligand ofP-gp plus a ligand of cytochrome P450 or a ligand of P-gp plus a ligandthat binds to both P-gp and cytochrome P450.

Characteristics of essential oils that reduce P-gp drug transport

When an essential oil is used in sufficient amount, the activity of P-gpwill be reduced; in particular P-gp drug transport back into theintestinal lumen will be reduced. Sufficient amounts would includeamounts necessary to increase integrated systemic concentrations overtime of the drug used in conjunction with the essential oil. Theconcentration of essential oil required to produce a sufficient amountof essential oil for inhibition of P-gp drug transport varies with thedelivery vehicle used for the essential oil and the drug. The luminalconcentration of the essential oil should be related to the drug's andessential oil's relative affinities for P-gp and the drug concentrationused. As the affinity of drug for P-gp increases, the requiredconcentration of the appropriate essential oil will increase. Mostessential oils of commercial application will decrease P-gp drugtransport by at least 10%, more preferably by at least 50%, and evenmore preferably by at least 75%.

In vitro P-gp Assays for Bioavailability

Any bioassay that determines whether a given composition inhibits P-gptransport can be used to identify preferred essential oils. A number ofsuch assays are set out below.

Everted Gut Assays

Everted intestine can be prepared by methods known in the art Hsing etal. Gastroenterology 1992; 102:879-85). In these studies rat smallintestines turned "inside out" (i.e. the mucosal (or luminal) surfaceturned outside and the serosal surface inside) are bathed in a drugcontaining solution with and without the addition of the essential oil.The serosal surface of the small intestine is bathed in a solution thatis periodically monitored or changed for the purpose of drug oressential oil measurement. For instance the everted rat small intestinescan be bathed in a physiological saline solution loaded with Rhodamine123 (Rh123) and the flux of Rh 123 monitored into the serosal solution.The addition of a essential oil in this set-up will increase Rh 123transport into the serosal solution. An increase in drug or Rh 123bioavailability will be determined as follows: ##EQU1## where Y is theinitial rate of Rh 123 transport, and X is the initial rate of rhodaminetransport in the presence of an essential oil. The initial rates will bedetermined as a linear relationship between time and Rh 123concentration in the luminal solution. Alternatively, the serosal sideof rat small intestines is bathed with the drug or essential oil ofinterest and the mucosal solution is monitored, as described in Hsing etal. (1992).

Selection of a P-gp Inhibitor Based on Cell Growth Assays

This assay can be used to select particularly preferred essential oils.Cells cultured with cytotoxic agents that are known P-gp transportsubstrates will be grown as controls in the absence of either drug oressential oil. The appK_(i) (apparent inhibition constant) for cellgrowth by drugs will be determined by varying the drug concentration inthe culture medium. The appK_(i) will be expressed as the concentrationof drug required to produce 50% inhibition of cell growth. Cells willalso be grown in the presence of drug and essential oil. The essentialoil will act to shift the appK_(i) to lower drug concentrationsnecessary for inhibition of cell growth. Cells with MDR can be used inthis assay as described in Hait et al., Biochemical Pharmacology 1993,45:401-406. The method sections of Hait et al. (1993) are hereinincorporated by reference. Preferred essential oils will decrease theappK_(i) for a drug by at least 2 times, more preferably by at least 3times, and even more preferably by at least 6 times at a non-toxicdosage.

Rhodamine (Rh 123) Cellular Assay of P-gp Drug Transport and DrugBioavailability

Rh 123 can be used in a cellular assay to monitor the bioavailability ofdrugs. Rh 123 transported by P-gp in this system acts as a drug, whereP-gp pumps the Rh 123 out of the cell. Single cells or a population ofcells can be monitored for the Rh 123 fluorescence which is indicativeof P-gp transport. The cell types used will contain a P-gp transporterfrom a MDR strain such as those listed in Nielsen and Skovsgaard,Biochimica et Biophysica Acta 1993; 1139:169-183 and herein incorporatedby reference. Cells are loaded with Rh 123 in the presence of 15nanograms per ml to 500 nanograms per ml of Rh 123 in a physiologicallycompatible buffer such as 3-N-morpholinopropanesulfonic acid (MOPS) withthe suitable concentrations of sodium, potassium, and calcium chlorideand an energy source. The cells are loaded with Rh 123 for 30-60 minutesdepending on the temperature (37° or room temperature). The loaded cellsare then washed and resuspended in buffer free of Rh 123. The efflux ofRh 123 can be determined using a fluorimeter. In the absence of anyessential oil Rh 123 will be pumped out of the cell due to the action ofP-gp, leading to a reduced amount of Rh 123 fluorescence from the cell.

Addition of a P-gp substrate or inhibitor either by preincubation afterthe cells have been washed with Rh 123 free buffer or during the effluxof Rh 123 from the cell will cause retention of Rh 123 within the cell.Retention of Rh 123 in the cell will be caused by the addition of anessential oil. Increased drug bioavailability is defined as the increasein Rh 123 retention within the cell. Compounds that increase Rh 123retention are essential oils.

Rh 123 retention in the absence of an essential oil will be determinedby total Rh 123 cell fluorescence minus background Rh 123 cellfluorescence. An increase in drug bioavailability due to the addition ofthe essential oil will be the percentage increase in Rh 123 fluorescenceretention as described by: ##EQU2## where X equals Rh 123 fluorescencein the presence of the essential oil minus the background Rh 123fluorescence and Y equals the Rh 123 fluorescence in the absence of theessential oil minus the background Rh 123 fluorescence.

The background Rh 123 fluorescence can be measured in a variety of waysincluding, but not limited to, the residual amount of Rh 123fluorescence at the end of the experiment, the residual amount of Rh 123fluorescence remaining based on an extrapolation of first order ratekinetics describing the efflux of Rh 123 from the cell, the residualamount of Rh 123 fluorescence in the presence of a sufficient amount ofmembrane detergents such as triton or digitonin, or the amount of Rh 123fluorescence in the presence of a potassium-valinomycin clamp.

The addition of both a second drug and an essential oil to the Rh 123assay will not necessarily cause an increased amount of Rh 123 retentioncompared to the presence of either the essential oil alone or the seconddrug alone. This is because Rh 123 retention can already be very highdue to the second drug or essential oil concentration. Extra retentiondue to the addition of either the second drug or the essential oil canbe difficult to measure above the signal for Rh 123 in the presence ofthe second drug or essential oil alone. However, once it has beendetermined that the drug (or second drug alone) increases Rh 123fluorescence, i.e. decreases Rh 123 efflux, it can be assumed that thedrug (or second drug alone) is transported by the P-gp transport system.

Vesicle Assays of P-gp Activity and Drug Bioavailability

A particularly preferred assay uses brush border membranes. Brush bordermembrane vesicles are prepared from the small intestine by methods knownin the art, such as, Hsing, S. et al., Gastroenterology 1992;102:879-885. The vesicles will be assayed for the presence of P-gp byusing monoclonal antibodies directed to P-gp either using SDS page gelelectrophoresis and western blotting techniques or using immunochemistryand electromicroscopy. Vesicles containing P-gp will be used for drugtransport assays.

Drug transport assays consist of measuring the transport of drugs intothe vesicles in an adenosine triphosphate (ATP) dependent fashion.Uptake of the drug in the presence of ATP will be monitored usingfluorescence or absorbance techniques, for instance using Rh 123 as thefluorescent drug transported into the interior of the vesicle.Radioactively labeled drugs can also be used to monitor drug transportinto the interior of the vesicle using a filter wash system. Theaddition of ATP will induce the transport of the drug into the vesicleand will increase drug transport compared to passive diffusion of thedrug into the vesicle interior. Addition of non-hydrolyzable analogs ofATP such as ATP gamma S or adenosine monophosphate para-nitrophenol(AMP-PNP) will not produce an ATP dependent influx of drug into thevesicle. Thus, the introduction of a non-hydrolyzable nucleotide can beused as a control to monitor whether drug transport has actuallyoccurred due to ATP hydrolysis from the P-gp transport system.

The addition of an essential oil to this assay system using afluorescent drug or a radioactive drug and monitoring its uptake, willreduce the uptake of the drug into the interior of the vesicle with theaddition of ATP. This reduction in drug transport represents an increaseof the bioavailability of the drug. The vesicles transporting drugs inan ATP-dependent fashion are oriented with the cystolic face of P-gpaccessible to the ATP. It is these vesicles that hydrolyze the ATP andtransport the drug into the interior of the vesicle. The interior of thevesicle in turn corresponds to the luminal surface or the apicalmembrane of the brush border cells. Thus, transport into the lumen ofthe vesicle or interior of the vesicle corresponds to transport into thelumen of the gut. A decrease in the transport of the lumen of thevesicle is the equivalent of increasing net drug absorption andincreasing the drug bioavailability.

P-gp ATPase Assays of P-gp Activity and Drug Bioavailability

P-gp molecules can be isolated in vesicles suitable for measuring ATPaseactivity. P-gp ATPase activity will be measured in the presence of othertypes of ATPase inhibitors, such as, but not limited to, sodiumpotassium ATPase inhibitors (ouabain and vanadate), mitochondrial ATPaseinhibitors such as oligomycin, and alkaline phosphatase inhibitors. TheATPase assays will also be conducted in the absence of sodium andpotassium to eliminate background sodium and potassium ATPase activity.ATPase activity will be measured as ATPase activity dependent on thepresence of a drug such as daunomycin. ATPase activity will be measuredusing ATP or hydrolyzable ATP analogs such paranitrophenolphosphate. Theproduction of product will be monitored using phosphate assay proceduresof those of Yoda, A. and Hokin, L., Biochem. Biophys. Res. Comm. 1970;40:880-886 or by monitoring phosphatase activity as recognized in theliterature.

A decrease in P-gp ATPase drug transport activity due to the addition ofan essential oil is recognized as an increase in drug bioavailability.P-gp molecules located in the brush border membrane vesicles areoriented so the cytosolic portion of the molecule finds and hydrolyzesATP. It is these P-gp molecules that will give rise to the drugdependent ATPase activity. An essential oil that is able to inhibit theATPase activity will be able to compete with the drug for the P-gptransport system. Such essential oils will decrease P-gp drug transportdue to their increased ability to inhibit P-gp activity. Preferably, anessential oil will increase drug bioavailability of orally administereddrugs by inhibiting gut P450 drug metabolism (preferably CYP3A) or gutP-gp drug transport or both. Preferably, a measure of the increase indrug bioavailability of an orally administered drug is the increase inthe AUC of a drug orally administered in the presence of an essentialoil compared to the absence of the essential oil, e.g. (Oral drug AUC inthe presence of an essential oil)--(Oral Drug AUC). More preferably, thefractional increase in drug bioavailability of a drug orallyadministered in the presence of an essential oil is the increase in drugbioavailability due to inhibition of gut drug metabolism and preferablynot due to the inhibition of non-gut drug metabolism. For example, thefractional increase in oral bioavailability can be calculated as:

    (Oral drug AUC in the presence of an essential oil/IV drug AUC in the presence of an essential oil)--(Oral Drug AUC/IV Drug AUC).

"Oral drug AUC" refers to the AUC of an orally administered drug. "IVdrug AUC" refers to the AUC of an intravenously administered drug. Thiscalculation is best applied to situations where the essential oil isminimally metabolized by the gut. Preferably, the increase in drugbioavailability (or oral drug bioavailability) related to the additionof an essential oil is at least 5%, more preferably at least 10% andmost preferably at least 30%.

Another manner of determining the amount of essential oil appropriatefor an oral formulation is based on the K_(i) of the specific inhibitor(for whichever binding is being measured). An appropriate amount ofinhibitor is one that is sufficient to produce a concentration of theessential oil in the lumen of the gut of the animal of at least 0.1times the K_(i) of the essential oil.

In all of these cases, the goal of selecting a particular concentrationis increased bioavailability of the pharmaceutical compound that isbeing administered. Thus, a desirable goal is to provide integratedsystemic concentrations over time of the pharmaceutical compound in thepresence of the inhibitor that is greater than the integrated systemicconcentrations over time of the pharmaceutical compound in the absenceof the inhibitor by at least 10% of the difference betweenbioavailability in its absence and complete oral bioavailability.Preferred is attaining of "complete bioavailability," which is 100%systemic bioavailability of the administered dosage.

Screening Assay for Superior Essential Oils

In summary, the various techniques described above for screeningcandidate essential oil compounds for activity levels by assaying forinhibition in the gut of a mammal of activity of a cytochrome P450enzyme or of transport by P glycoprotein are all generally useful asmethods of identifying compounds that are most useful for increasingbioavailability of a drug in a mammal. In all of these assays, the bestessential oils are those compounds selected from the candidate compoundsbeing tested that best inhibit either transport or enzymatic destruction(preferably the latter) of a tested drug in the gut of the mammal(either by direct testing in vivo or by a test that predicts suchactivity). When testing for inhibition of activity of a cytochromeenzyme, assays that detect inhibition of members of a cytochrome P450 3Afamily (for a particular mammal, particularly human) are preferred.Although in vivo assays are preferred, because of the directrelationship between the measurement and gut activity, other assays,such as assays for inhibition of cytochrome P450 activity in isolatedenterocytes or microsomes obtained from enterocytes of the mammal inquestion or for inhibition of cytochrome P450 in a tissue or membranefrom the gut of said mammal, are still useful as screening assays. Thesame ordering of preferred screening assays (i.e., in vivo beingpreferred over in vitro) is also preferred for screening of inhibitionof P-gp transport. Screening by assaying for both inhibitions ispreferred, with inhibition of cytochrome P450 activity generally beingmore important than that of P-gp-mediated transport.

Coadministration and Delivery of Essential oils

Coadministration of an Essential Oil and a Drug

The present invention will increase the bioavailability of a drug insystemic fluids or tissues by co-administering the essential oil with adrug. "Coadministration" includes concurrent administration(administration of the essential oil and drug at the same time) andtime-varied administration (administration of the essential oil at atime different from that of the drug), as long as both the essential oiland the drug are present in the gut lumen and/or membranes during atleast partially overlapping times. "Systemic fluids or tissues" refersblood, plasma, or serum and to other body fluids or tissues in whichdrug measurements can be obtained.

Delivery Vehicles and Methods

Coadministration can occur with the same delivery vehicle or withdifferent delivery vehicles. The essential oil and the drug can beadministered using, as examples, but not limited to, time releasematrices, time release coatings, companion ions, and successive oraladministrations. Alternatively, the drug and the essential oil can beseparately formulated with different coatings possessing different timeconstants for release of essential oil and drug.

In addition to simply being mixed with the drug being protected in apharmaceutical composition the essential oils can also includecombinations of compounds of different properties. For example, a firstcompound can act as a P-gp inhibitor while a second compound acts as aCYP3A inhibitor. Essential oils can also be bound to the drug beingprotected, either by covalent bonding or by ionic or polar attractions.

Essential oils also increase bioavailability when used with epitheliatissues other than the gut. The discussion above of the invention asused in the gut is appropriate for other types of epithelia. Forexample, CYP 3A enzymes and P-glycoprotein are present in the skin, andessential oils can be used in transdermal formulations to increase drugbioavailability to systemic fluids and tissues. Such applications arepart of the invention, since inhibition of CYP 3A enzymes andP-glycoprotein by essential oils in epithelia other than the gutprovides the same mechanism of action.

Formulations of Essential oils

The invention is carried out in part by formulating an oralpharmaceutical composition to contain an essential oil. This isaccomplished in some embodiments by admixing a pharmaceutical compound,usually a pharmaceutical carrier, and an essential oil, the essentialoil being present in an amount sufficient to provide integrated systemicconcentrations over time of the compound (as measured by AUC's greaterthan the integrated systemic concentrations over time of the compound inthe absence of the composition) when the pharmaceutical composition isadministered orally to an animal being treated. A pharmaceutical carrieris generally an inert bulk agent added to make the active ingredientseasier to handle and can be solid or liquid in the usual manner as iswell understood in the art. Pharmaceutical compositions produced by theprocess described herein are also part of the present invention.

The present invention can also be used to increase the bioavailabilityof the active compound of an existing oral pharmaceutical composition.When practiced in this manner, the invention is carried out byreformulating the existing composition to provide a reformulatedcomposition by admixing the active compound with an essential oil, theessential oil being present in an amount sufficient to provideintegrated systemic concentrations over time of the compound whenadministered in the reformulated composition greater than the integratedsystemic concentrations over time of the compound when administered inthe existing pharmaceutical composition. All of the criteria describedfor new formulations also apply to reformulation of old compositions. Inpreferred aspects of reformulations, the reformulated compositioncomprises all components present in the existing pharmaceuticalcomposition plus the essential oil, thus simplifying practice of theinvention, although it is also possible to eliminate existing componentsof formulations because of the increase in bioavailability. Thus, theinvention also covers reformulated compositions that contain less thanall components present in the existing pharmaceutical composition plusthe essential oil. However, this invention does not cover alreadyexisting compositions that contain a component which increasesbioavailability by mechanisms described in this specification (withoutknowledge of the mechanisms), should such compositions exist.

Traditional formulations can be used with essential oils. Optimalessential oil doses can be determined by varying the amount and timingof essential oil administration and monitoring bioavailability. Once theoptimal essential oil dose is established for a drug, the formulation(essential oil, drug, and other formulation components, if any) istested clinically to verify the increased bioavailability. In the caseof time- or sustained-release formulations, it will be preferred toestablish the optimal essential oil dose using such formulations fromthe start of the bioavailability experiments.

Many of the essential oils have been used in flavorings under manydifferent circumstances, and it is possible that they have been used asflavorings in pharmaceutical compositions. However, flavorings are usedin small quantities, and such materials are not likely to approach eventhe outer limits of the present invention as defined by thespecification and claims. In particular, preferred formulations of theinvention contain at least 1% by weight essential oil relative to thetotal weight of the formulation (including the capsule, if present),more preferably at least 2%, even more preferably at least 5%. In mostcases essential oils used as flavorings are used at less than 0.1% ofthe materials they are being used to flavor. In considering thesepercentages, it should be recalled that these are percentages of theformulation in which the active ingredient is being presented, notpercentages by weight or volume as concentrations in the medium in whichthe pharmaceutical composition will become dissolved or suspended afteringestion of the formulation (the latter being the % values shown atother locations in this specification, such as in Table 1). Furthermore,since many essential oils as well as many of the essential oilcomponents are liquids, such materials will often be used in capsules(either hard or soft standard pharmaceutical gel capsules, for example).Flavorings have generally not been used with capsules, since the capsuleprotects the user from any disagreeable flavor or odor resulting fromthe active pharmaceutical compound or other components of theformulation that are present. Presentation of an essential oil in apharmaceutical capsule is thus a preferred embodiment of the invention.

Table 4 sets forth a number of exemplary formulations to illustrate theinvention. Two essential oils are shown in the formulations, peppermintoil and carrot seed oil, that have similar rates of inhibition (56% forpeppermint oil at a concentration of 0.0001% in the assay medium, and52% for carrot seed oil at the same concentration). A simple calculationbased on the % inhibition values of Tables 1 or 2 or on assay data forcompounds not listed in the Tables would proved the amount of otherinhibitors necessary to provide the same effect. The other ingredientsshown in the formulations are standard ingredients used inpharmaceutical compositions and can be readily substituted by otheranti-oxidants, surface active agents (SSA), etc. In Table 4, "alphatocoph" is alpha-tocopherol, "BHA" is butylated hydroxy anisole, "PVP"is polyvinylpyrrolidone, "Klucel" is hydroxypropyl cellulose, a "bilesalt" is cholic acid and/or its sodium salt or a similar salt of a bileacid such as deoxycholic acid or glycholic acid, "Tween" is acommercially available surfactant of the Tween class such as Tween 21 or81, and "fatty acid" is a naturally occurring fatty acid or a simple(e.g., ethyl) ester thereof.

                                      TABLE 4    __________________________________________________________________________    FORMULATION EXAMPLES-CYCLOSPORINE                  A  B  C  D   E   F   G  H    __________________________________________________________________________    CYCLOSPORINE  100                     100                        100                           100 100 100 100                                          100    ANTI-OXIDANT    ALPHA TOCOPH  180                     180                        180                           180    BHA                 0.7                           0.7 0.7 0.7 0.7                                          0.7    INHIBITOR    PEPPERMINT OIL                  100                     100                        100                           100    CARROT SEED OIL     100                           100 200 200 200                                          200    ANTINUCLEATING AGENT    PVP           175                     175                        87.5                           87.5                               87.5    KLUCEL              87.5                           87.5                               87.5                                   175 175                                          175    SAA    BILE SALT     3.5   3.5                           1.75                               1.75                                   1.75    TWEEN            3.5   1.75                               1.75                                   1.75                                       3.5                                          3.5    SOLVENT    ETHYL ALCOHOL 141.5                     141.5 40.8    220.8  220.8    FATTY ACID          40.8   220.8   220.8    TOTAL WT.     700                     700                        700                           700 700 700 700                                          700    __________________________________________________________________________

The invention now being generally described, the same will be betterunderstood by reference to the following detailed example, which isoffered for illustration only and is not to be considered limiting ofthe invention unless otherwise specified.

EXAMPLE Inhibition of Drug Degradation by Essential Oils

Induction of rat cytochrome P4503A with dexamethasone

Ten male Sprague-Dawley rats (250-300 g; Bantin Kingman) receiveddexamethasone (100 mg/kg) each day for 4 days by intraperitonealinjection of a dexamethasone suspension in corn oil. On day 5 rats weresacrificed by decapitation, and the livers were excised and perfusedwith 0.15 M potassium chloride solution until free of blood. Perfusedlivers were maintained on ice during all subsequent manipulations.

Preparation of rat liver microsomes

Perfused livers were manually homogenized with 0.1 M phosphate buffer(pH 7.4) then the homogenates were centrifuged at 9,000 g for 20minutes. Supernatants from the initial centrifugation were transferredto ultracentrifuge tubes and centrifuged at 100,000 g for 60 minutes.Supernatants from the ultracentrifugation were discarded, and theresidual microsomal pellet was suspended in 0.15 M potassium chloride(approximately 25 ml) and centrifuged at 100,000 g for 30 minutes. Thesupernatant was again discarded, and the microsomal pellet was suspendedin 0.1 M phosphate buffer. Then the protein and cytochrome P450concentrations of the microsomal suspensions were determined using themethods of Bradford (M. Bradford Anal. Biochem. 72:248 1976!) and Omuraand Sato (T. Omura and R. Sato J. Biol. Chem. 239:2370 1964!)respectively. Microsomal suspensions were stored at -80 ° C. prior touse in metabolic incubations.

Microsomal incubations

Rat liver microsomes (250 μg/ml), diethylenetetraminepentaacetic acid (1mM), cyclosporine (1 μM; 0.0001%), and either the candidate metabolicinhibitor (0.01%, 0.001%, 0.0001%) or the solvent in which it wasdissolved (ethanol or buffer) in 0.1 M phosphate buffer pH 7.4 (totalvolume of 990 μl) were preincubated for 5 minutes at 37° C. inborosilicate glass culture tubes (16 mm×100 mm) using a reciprocalshaking water bath with a constant shaking rate of 100 rpm. Metabolicreactions were started by addition of nicotinamide adenine dinucleotidephosphate (1 mM) to give a total reaction volume of 1 ml. Reactions wereconducted in triplicate and were compared to controls withoutnicotinamide adenine dinucleotide phosphate. Incubations were allowed toproceed for 25 minutes, and the metabolic reactions were stopped byaddition of 50:50 acetonitrile:water saturated with zinc sulfate (2 ml)and 100 μl of rotenone internal standard solution (10 μg/ml in reagentalcohol). Samples were vortex mixed for 10 seconds, and then centrifugedfor 10 minutes at 5,500 rpm. Supernatants were decanted to new culturetubes, hexane (2 ml) was added, and the mixtures were vortex mixed for60 seconds. Hexane-washed samples were centrifuged for 5 minutes at5,500 rpm, and then the upper hexane layer was removed by aspirationthrough a borosilicate glass Pasteur pipette. The remaining solution wassubjected to solid-phase extraction.

Solid-phase extraction

Bond-Elut® LRC C-18 solid-phase extraction columns were fitted to a VacElut SPS 24 vacuum manifold (both from Varian Sample PreparationProducts, Harbor City, Calif., U.S.A.), and then washed with 2 mlreagent alcohol followed by 2×2 ml distilled water. Hexane-washedsupernatants above were drawn onto the washed Bond-Elut® columns by highvacuum, and then the columns were washed with 2×1 ml water and thesamples eluted with 1 ml acetonitrile. Acetonitrile solutions wereevaporated to dryness under nitrogen, and then dry samples werestoppered and stored frozen until analysis by reverse-phase highpressure liquid chromatography.

Analysis of cyclosporine and metabolites

Reverse-phase high pressure liquid chromatographic analysis ofcyclosporine and metabolites from microsomal incubation mixturesutilized a Beckman model 126 binary solvent module, a Beckman model 168diode-array ultraviolet absorbance detector, and a Beckman model 507autosampler with a Rheodyne model 7010 sample injection valve (100 μlsample loop). Data collection and analysis utilized Beckman System Gold™Personal™ Chromatography Software loaded onto an IBM model 350 466DX2computer.

Extracted and dried samples from incubation experiments werereconstituted in 65:35 acetonitrile:water (500 μl), and then 100 μl wereinjected onto a Beckman Ultrasphere® RP-18 analytical column (5 μm; 4.6mm×250 ram) maintained at 70° C. with an Alltech Adsorbosphere®Direct-Connect™ guard-cartridge system in line with, but not directlyattached to, the column. Cyclosporine and metabolites were separatedusing an acetonitrile-water (pH 3) solvent gradient (65% acetonitrile×4minutes followed by a 1% per minute increase to 75% acetonitrile whichwas maintained for 6 minutes) and a solvent flow rate of 1 ml/minute.Cyclosporine and metabolite(s) were detected by ultraviolet absorbanceat 214 nm. Rotenone internal standard eluted at 5.6±0.4 minutes, thecombined AM1 and AM9 (cyclosporine hydroxylated metabolites) peak elutedat 8.3±0.4 minutes, and cyclosporine eluted at 16.1±0.5 minutes.

Data analysis

Peak areas for cyclosporine, the combined AM1 and AM9 cyclosporinehydroxylated metabolites peak (AMI&AM9), and the rotenone internalstandard were determined from the high pressure liquid chromatographydata by integration using Beckman System Gold™ Personal™ ChromatographySoftware. Cyclosporine metabolism was measured as the peak area ratio ofthe combined AMi&AM9 peak to the parent cyclosporine, and then thepercentage inhibition of cyclosporine metabolism by the candidateinhibitor was determined using the following formula:

    Percentage metabolism=100×(1-inhibitor/vehicle)

where "inhibitor"=AMI&AM9/CyA peak area ratio from samples treated withinhibitor and "vehicle"=AMI&AM9/CyA ratio from samples treated with thevehicle (either ethanol or buffer) in which the inhibitor was dissolvedfor addition to the incubation mixture. Each incubation was conducted intriplicate, and inhibition data are reported as the mean ± standarddeviation (SD).

Results of Inhibition Assays

The results of these assays are set out in Tables 1-3 above, in whichTable 1 shows assay results using essential oils at the statedconcentrations, while Tables 2 and 3 show the results of assays usingindividual components of essential oils as well as the comparison valuesobtained using the solvents in which the essential oils were dissolved(i.e., negative controls) or ketoconazole, a previously known inhibitor.Essential oils and essential oil components are identified by ChemicalAbstracts numbers (CAS#) and by GRAS identifiers as set out in volume 21of the Code of Federal Regulations (CFR#), as well as by common andscientific names. The concentration of oil or other component used inthe assay is shown in wt % in the heading of the appropriate columns,with the % inhibition being shown for the various bioenhancers (anegative value indicates that the component being tested actuallyreduces bioavailability). In some cases individual assays were repeatedand the results are shown. "Obscured," which appears in some columns,means that metabolite peaks were not readily measurable because of thepresence of unknown interfering substances in the essential oils.

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference. The inventionnow being fully described, it will be apparent to one of ordinary skillin the art that many changes and modifications can be made theretowithout departing from the spirit or scope of the appended claims.

We claim:
 1. A method for reducing P-glycoprotein-mediated membranetransport of a pharmaceutical compound administered to a patient, themethod comprising:coadministering the pharmaceutical compound andbenzoin gum to the patient in an amount sufficient to provide increasedinhibition of P-glycoprotein-mediated membrane transport of saidpharmaceutical compound in the presence of the benzoin gum relative toP-glycoprotein-mediated membrane transport of said pharmaceuticalcompound in the absence of the benzoin gum, wherein the benzoin gum hasan activity of at least 10% inhibition at a concentration of 0.01 wt. %or less in an assay that measures reduced conversion of cyclosporine tohydroxylated products using an assay system containing 250 μg rat livermicrosomes, 1 μM cyclosporine, and 1 mM reduced nicotinamide adeninedinucleotide phosphate (NADPH) in 1 ml of 0.1M sodium phosphate buffer,pH 7.4.
 2. The method of claim 1, wherein the pharmaceutical compoundand the benzoin gum are orally coadministered.
 3. The method of claim 2,wherein said pharmaceutical compound comprises taxol.
 4. The method ofclaim 1, wherein said pharmaceutical compound comprises taxol.
 5. Acomposition comprising benzoin gum and taxol in a pharmaceuticallyacceptable carrier.
 6. The composition of claim 5, wherein thecomposition is orally administrable to the patient.
 7. The compositionof claim 5, wherein the benzoin gum is present in an amount having anactivity of at least 10% inhibition at a concentration of 0.01 wt. % orless in an assay that measures reduced conversion of cyclosporine tohydroxylated products using an assay system containing 250 μg rat livermicrosomes, 1 μM cyclosporine, and 1 mM reduced nicotinamide adeninedinucleotide phosphate (NADPH) in 1 ml of 0.1M sodium phosphate buffer,pH 7.4.